1. Field of the Invention
The present invention generally relates to a common rail such as a high-pressure fuel manifold in an accumulator system fuel injection system of a diesel internal combustion engine, and particurally, relates to a common rail for a diesel engine made by firmly fixing a branching connection body to a common rail body by a frictin welding (a friction pressure welding).
2. Description of Related Art
As a common rail for a diesel engine, one having a common rail body integrally formed with a branching connection body by a forging method or one having a common rail body connected to a branching connection body (a branching connection fitting) by a welding method (including a friction wielding method) has been known. Among them, as a common rail for a diesel engine in a system of integrally manufacturing a common rail body and a branching connection body by the forging method, for example, a common rail (refer to JP-A-6-109191) as shown in FIG. 21 has been known, in which a short tubular wall (a branching connection body) 21-2 is integrally projected at a peripheral wall in an axial direction of a common rail body 21 made of hot forging of a solid core round bar material; a through hole 21-3 communicated with a distribution hole 21-2 bored on the common body 21 by a gun drill or the like is formed on this tubular wall 21-1; a pressure bearing surface 22-2 made by a connection head 22-1 of a branch tube 22 supplying a fuel to an injection nozzle (not illustrated) of each cylinder engine is abutted and joined to a pressure receiving bearing surface 21-4 opening to the outside that is disposed at the front end of the through hole 21-3; and a nut for fastening (a hexagon cap nut) 23 incorporated in the side of the branch tube 22 in advance is screwed together in the tubular wall 21-1. Thereby, this common rail is fastened and connected due to the pressure under the neck of the connection head 22-1.
In addition, as a common rail for a diesel engine in a system of connecting the branching connection body (a branching connection fitting) to the common rail body by the welding method, for example, a common rail (refer to JP-A-9-236064 and JP-A-9-280460) as shown in FIG. 22 has been known, in which a through hole 31-2 communicated with a distribution hole 31-1 of a common rail body 31 is formed at an outer circumferential face in an axial direction of the common rail body 31 made of a thick steel pipe; a branching connection body (a branching connection fitting) 34 having a through hole 34-1 communicate with this through hole 31-2 formed thereon is pressure-bonded (it is pressure-bonded in as a whole, however, it may partly melt and be fusion-bonded) by a projection welding or a TIG welding or an ark such as a plasma or as shown in FIG. 23, by a friction welding (a friction pressure bonding); the pressure bearing surface 22-2 made by the connection head 22-1 of the branch tube 22 supplying the fuel to the injection nozzle (not illustrated) of each cylinder engine is abutted and jointed to a pressure receiving bearing surface 34-2 opening to the outside that is disposed at the front end of the through hole 34-1 of the branching connection body (the branching connection fitting) 34; and a nut for fastening (a hexagon cap nut) 23 incorporated in the side of the branch tube 22 in advance is screwed together in the branching connection body (the branching connection fitting) 34. Thereby, this common rail is fastened and connected due to the pressure under the neck of the connection head 22-1.
However, in the case of the common rail in the system of fusion-bonding the branching connection body (the branching connection fitting) to the common rail body by a projection welding or a TIG welding or an ark such as a plasma as shown in FIG. 22 among the above-described common rails for the diesel engine, a fusion nugget 35 is disposed at a welding part, and an intense stress is generated at a boundary with a no-fusion part upon congelation in this welding part. Therefore, this common rail has a problem such that there is a high possibility that a crack is generated in association with the stress due to the external force or this common rail is destroyed, and the fusion part itself has a poor reliability with respect to the outer force such as oscillation, the inner pressure, and bending because its ligament force is decreased. In addition, in the case of the common rail in the system of firmly fixing the branching connection body (the branching connection fitting) to the common rail body by the friction welding (the friction pressure welding), as shown in FIG. 23, confronting the branching connection body (the branching connection fitting) 34 to a flat surface 31-3 formed on the outer face of the common rail body 31, the branching connection body is bonded to the common rail body by means of heat generation due to the friction between one flat face and the other flat face and upset. Therefore, there is a case that a squeeze-out affect of efficiently discharging a stain on a bonding part and an oxide or the like to the outside of the bonding part cannot be sufficiently obtained, so that there is a high possibility that carbide, an oxide, and a void or the like remain at the bonding part. Therefore, as same as the above case, this involves a problem such that a reliability of the bonding part with respect to the outer force such as oscillation, the inner pressure, and bending is poor.